The present invention relates to an image reading apparatus, an image processing apparatus, and a method therefor and, more particularly, to an image reading apparatus, an image processing apparatus, and a method therefor using a linear image sensor for performing an intra-pixel transfer/read-out operation.
Conventionally, as a color image reading apparatus using a linear image sensor, an apparatus with the arrangement shown in FIG. 1 is known.
In the color image reading apparatus shown in FIG. 1, an original 212 on an original table glass 211 is illuminated with light using an illumination light source 210 and a reflector 209, and light reflected by the original is imaged on the light-receiving surface of a CCD (color linear image sensor) 201 via a first mirror 208, a second mirror 205, a third mirror 206, and a lens 202. When a portion surrounded by a broken line 207 in FIG. 1 is moved at a velocity V in the direction of an arrow in FIG. 1, and a portion surrounded by a broken line 203 is moved at a velocity V/2 in the direction of an arrow in FIG. 1, the entire image on the original 212 can be read by the CCD 201.
FIG. 2 shows the arrangement of the CCD linear image sensor 201 used in the conventional color image reading apparatus.
Referring to FIG. 2, reference numerals 301, 302, and 303 denote light-receiving units respectively having R (red), G (green), and B (blue) color filters. In each light-receiving unit, diodes for converting photons into charges (electrons in this case) are arranged in units of pixels. Charges generated by light reception for a predetermined period of time are respectively transferred (shifted) to CCD transfer units (charge transfer units) 304, 306, and 308 for ODD pixels and CCD transfer units (charge transfer units) 305, 307, and 309 for EVEN pixels. The charges transferred (shifted) to the CCD transfer units are sequentially transferred in a predetermined direction in the corresponding CCD transfer units while the light-receiving units perform light-receiving and charge storage operations for the next line, and are sequentially converted into voltage signals by amplifiers 310 to 316. Then, these voltage signals are output.
However, as shown in FIG. 2, in the conventional color linear image sensor, since the CCD transfer units for charge transfer are arranged between adjacent ones of the R, G, and B light-receiving units, the interval between the R and G light-receiving units and the interval between the G and B light-receiving units shown in FIG. 2 must be set to be large.
When the interval between adjacent light-receiving unit increases, a memory for correcting the reading positions of R, G, and B signals is required when read R, G, and B signals are subjected to color correction processing such as masking calculations. In this case, as the intervals of the R, G, and B light-receiving unit become larger, the required memory capacity undesirably increases.
Recently, a structure wherein CCD transfer units are disposed to sandwich light-receiving units of different colors therebetween in place of being disposed adjacent to the corresponding light-receiving units is proposed (Japanese Patent Application Nos. 6-187157 and 6-197075).
FIG. 3 shows the arrangement wherein the CCD transfer units are disposed to sandwich the light-receiving units of different colors therebetween. In this case, since the CCD transfer units need not be disposed between the adjacent light-receiving units of the respective colors, the interval between the adjacent ones of the R, G, and B light-receiving units can be greatly reduced and the required memory capacity can also be reduced as compared to a conventional sensor.
However, received and stored charges must be transferred (shifted) to the CCD transfer units via the light-receiving units (pixels) of different colors. When so-called intra-pixel transfer is performed, since each light-receiving unit is receiving light reflected by an original image while charges are passing through the light-receiving units of different colors, color mixing may occur upon transfer.